proected empty constructor for Sesson class

I'd like to create a wrapper implementation and subclass of the Session class.
This wrapper is by default stateless, delegating behaviour to a true Session object.
This is useful for example to start global transactions around the next methods.

Currently Session has two constructor that can only create 'true' Sessions.

An empty protected constructor may suffice.

In fact, it's not clear why there is a SessionFactory interface when actually one cannot modify or decorate the default Session implementation.